Extraction of gold from dilute solutions



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nx'raao'rronor some FROM DILU'IE sotorrons Myinveution' relates-to the extraction and recovery of gold from. diluteisolutions, and

1 of gold from dilute solutions by contactwith tellurium in amorphous condition:. It has long been known .that when a metal is brought in contact with a solution of suitable concentration of a salt of a more elcctro-negative metal the more electro-pos itive metal tends to dissolvepwhlle a chemically equivalentamount of the more electronegative metal tends to be deposited. A

familiar example ofthis tendency is the forming of a stain of copperjwhen a drop ofa'solution of coppersulphate is placed on a knife blade; and the precipitation of I silver and lead by 'Zinc arei'other familiar lit) examples. The ;rule that any metal will, under favorable conditions, precipitate from solution any more electro-negative metal is a general one,-and-it is well known that metallic tellurium will precipitate gold from solution, in accordance with this general rule. I

I have discovered that tellurium in the mossy or amorphous condition in which it exists after preciptation from solution has many advantages as a precipitating agent over tellurium in its usual crystalline or me tallic condition and is many times as efficient as a precipitating agent, and is capable of rapidly extracting gold from solutions of very great dilution.

' In the preferred'form of my invention,v I

first prepare a dilute solution of a suitable.

salt of tellurium, such as tellurium chloride for example, and I then precipitate the telluriumfrom this solution by a reagent such as sulfur dioxide. The tellurium slowly separates'from the solution asa black precipitate of extreme fineness, and this precipitate, after being lightly compacted to give it somewhat increased density, forms a mass of high porosity. By passing "a highly dilute solution of gold chloride or equivalent solu ble salt of gold through a porous layer of amorphous precipitated tellurium prepared in the manner described and supported in any convenient Way, Isecurethe practically instantaneous and completeirecovery of the gold present in the solution.

It will of course be evide'ntlthat where the dilute gold solution contains insoluble particles, the previous filtration of the gold solution is desirable to prevent the contami nation and clogging of the porous tellurium i Y Application filed February 12,1925. Serial No. 8,831.

or dissolving effect upon the'porous mass of, amorphous v tellurium, th s tendency can be corrected by adding to the dilutegold solution a small amountlof a protecting agent.

.Ighave found sulfur dioxidc tobe a particularly satisfactory andetlicient protecting 7 agent; and a very small amount of sulfur dioxide dissolved in the dilute gold solution is desirable to. protect the amorphous tellurium from loss of activity. 7

The gold which is. precipitated from solution by filtration through a porous massj o-f-amorphous tellurium in the manner de. scribed may be recovered by heatingthe tel- .lurium mass to a temperature above; the

volatilizing temperature of tellurium, and the volatilized tellurium -may-be recovered and reused.

It will be evident that many modifications I may be made, without departing from the essential features of the invention as herein disclosed. Althoughin the preferred form of my invention I pass the dilute gold solu- 'tion to be treated through a fixed mass of amorphous percipitated"tellurium, it will of course be evident that it is the contact. between the very finely'divided tellurium and the dilute gold solutionwhich is important, and that stirring the finely divided precipitated tellurium in the dilute gold solution, or precipitating the tellurium within the dilute gold solution, represent equivalent processes. In still another form of my inven" tion I first impregnate a porous mass of earthenware or "other equivalent material with a solution of a compound of tellurium soluble inwater, and I then precipitate amor phous tellurium within the pore spaces of the porous body by the use of any suitable reagent, in much the same manner that semipermeable membranes are made by precipitating' copper fcrrocyanide within the pores of earthenware by the reaction between a soluble salt of copper and a solution of a suitable ferrocyanide. A porous mass made as described may conveniently "be used as a support for an additional quantity of amorphous precipitated tellumum, and instead of a porous support of earthenware being used, the same principle may be used to impregnate cloth or other a fabric with precipitated amorphous tellurium. I find the use of a fixed, slightly compacted layer of the amorphous precipi tated tellurium, resting ona porous support and surmounted by a pie-filtering or protecting porous layer represents the most desirable arrangement for the rapid filteringfof large volumes of dilute gold solutions under ordinary conditions.

Instead of obtaining tellurium in amorphous condition by precipitating a solution of a soluble compound of tellui'ium by sulfurous acid or asoluble sulfite or equivalent reducing agentil may obtain finely divided t'ellurinu'i porous condition by attrition in a"colloid mill or equivalent apparatus, and tellurium so obtained may be used las a filtering agent, oither alone or preferably admixed with amorphous tellnrium' prepared vby the action of: reducing agents on solutions of a' soluble compound of telluriuin. Althougl i'I prefer'to employ sulfur dioxide or snlfurous acid as my reducing'agent in the precipitation of tellurium from solutions of its soluble compounds, I ai'n aware that many other active reouoing agent s maybe employed in the preparation of the amorphous precipitated material, and; that under favorable conditions Qlectrolytic reduction may also be employed instead of the use of chemical reducing re- 1. The process of extracting gold from' dilute solutions which comprises passing a ;dilute solution ofv gold through a porous mass of amorphous precipitated tellnrium.

2/1116 process of entracti'ngfgold from dilute solutions-Which comprises contacting a dilute gold solution with tellurium 'in' amorphous precipitated condi tion.

3'. The process ot extracting gold from dil ute solutions whichfcomprises I contacting a dilute gold solut on"containing' sulfur.

dioxide with telluriuni in amorphous precipitated condition.

4. The process which comprises filtering a dilute aqueous solution containing gold and contacting the filtered solution with telluriu n 1n amorphous condition.

' In testimony whereof have hereunto subscribed my name .February, 1925.

7 this 10th day WALTER lo. simianin}. 

